The present invention relates generally to semiconductor packaging using surface-mount technologies (SMTs), and, more particularly, to an exposed pad packaged power semiconductor device.
Packaged power semiconductor devices are commonly used to implement switches and rectifiers in power electronics. In order to assemble a typical power semiconductor package, a power die is mounted on a lead frame die paddle (also known as a flag) using solder paste. The solder paste is then reflowed at a relatively high temperature (e.g., >350° C.) to form a mechanical bond between the power die and the die paddle. Due to the relatively good thermal conductivity properties of the solder, the solder acts as a heat sink that dissipates heat emitted from the power die during operation of the semiconductor device.
After the solder reflow, a control die is mounted to another die paddle of the lead frame using die-attach epoxy that is subsequently cured in an oven at a lower temperature (e.g., 175° C.). The power die and the control die then are electrically connected to one another and to metal leads of the lead frame with bond wires.
Following wire bonding, the assembly (including the power die, control die, metal leads, and bond wires) is mostly encapsulated in molding compound, leaving the distal ends of the leads exposed, and then the molding compound is cured. After encapsulation, the power semiconductor package is singulated (the process of separating adjacent, simultaneously assembled devices) to make a power semiconductor package that is ready for mounting on a circuit board. Singulation also includes cutting and/or removing support structures that were used to hold the metal leads in place.
The need to perform two separate die attach processes, one for the power die with solder and one for the control die with adhesive, adds time and cost to the assembly process. Accordingly, it would be advantageous to be able to assemble a power semiconductor device with just a single die attach step.